Interactive effects of cyclic oxidation and structural evolution for Ti-6Al-4V/(TiC+TiB) alloy composites at elevated temperatures

A kind of Ti-6Al-4V alloy matrix composite with coupled (TiC+TiB) networks as reinforcements was conceived and actually prepared by reaction hot pressing technique. Its internal microstructures transferred from Widmanstätten lamellae into equiaxed α-Ti grains during in-situ synthesizing reactions, which were characterized by HRTEM analyses to reveal the crystallographic correlations. With an effort to enhance its high-temperature oxidation resistance, the cyclic oxidation kinetics and concomitant structural evolution were experimentally investigated and thermodynamically elucidated in the 873–1073 K temperature range. The specially designed network configuration of hybrid reinforcers was found to improve the oxidation resistance to a remarkable extent. The cyclic oxidation kinetics followed the classic parabolic relation at the relatively lower temperature of 873 K, but this was replaced by a linear trend once temperature rose up to 1073 K. It was revealed that the thermal-stress induced spallation of oxide scales was the dominant factor to modulate the interaction of oxidation kinetics and structural evolution. A phenomenological model of oxide scale growth was proposed accordingly to depict the kinetics transition of cyclic oxidation process.